U.S. patent application number 14/911415 was filed with the patent office on 2016-07-14 for surface-modified separation membrane and method for modifying surface of separation membrane.
The applicant listed for this patent is INDUSTRY-UNIVERSITY COOPERATION FOUNDATION HANYANG UNIVERSITY, LG ELECTRONICS INC.. Invention is credited to Hyowon KIM, Jeongil KYE, Changho LEE, Hobum PA.
Application Number | 20160199788 14/911415 |
Document ID | / |
Family ID | 52778929 |
Filed Date | 2016-07-14 |
United States Patent
Application |
20160199788 |
Kind Code |
A1 |
LEE; Changho ; et
al. |
July 14, 2016 |
SURFACE-MODIFIED SEPARATION MEMBRANE AND METHOD FOR MODIFYING
SURFACE OF SEPARATION MEMBRANE
Abstract
A surface-modified separation membrane of the present invention
comprises a separation membrane, and a coating layer formed on the
surface of the separation membrane for improving the contamination
resistance and chemical resistance of the separation membrane,
wherein the coating layer is implemented with a nanoscale thickness
of the coating layer in order to inhibit a decrease in permeation
flux of the separation membrane before and after coating the
coating layer, and comprises: dopamine for providing, to the
coating layer, an adsorption force to be bound stably with the
separation membrane; and a hydrophilic material which is bound to
the dopamine through secondary bonding or cross-linking containing
a hydrogen bond in order to inhibit the deterioration of the
durability of the coating layer, and provides hydrophilicity to the
surface of the separation membrane in order to protect the
separation membrane from hydrophobic contaminants. A method for
modifying the surface of a separation membrane of the present
invention comprises the steps of: injecting a separation membrane
to be surface-modified into a reactor; adding a mixture solution,
which is formed by adding a hydrophilic material to a Tris-buffer
solution having an adjusted pH range at which dopamine reacts and
stirring the same, to the reactor; adding dopamine and an
initiator, which induces the cross-linking of the hydrophilic
material and dopamine, to the reactor at a predetermined
temperature range; and forming a coating layer comprising dopamine
and the hydrophilic material on the separation membrane through
thermal cross-linking at the predetermined temperature range while
injecting oxygen into the reactor.
Inventors: |
LEE; Changho; (Seoul,
KR) ; KIM; Hyowon; (Seoul, KR) ; KYE;
Jeongil; (Seoul, KR) ; PA; Hobum; (Seoul,
KR) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
LG ELECTRONICS INC.
INDUSTRY-UNIVERSITY COOPERATION FOUNDATION HANYANG
UNIVERSITY |
Seoul
Seoul |
|
KR
KR |
|
|
Family ID: |
52778929 |
Appl. No.: |
14/911415 |
Filed: |
October 1, 2014 |
PCT Filed: |
October 1, 2014 |
PCT NO: |
PCT/KR2014/009289 |
371 Date: |
February 10, 2016 |
Current U.S.
Class: |
210/500.33 ;
427/244 |
Current CPC
Class: |
B01D 65/08 20130101;
B01D 67/0088 20130101; B01D 2323/02 20130101; B01D 2323/30
20130101 |
International
Class: |
B01D 67/00 20060101
B01D067/00; B01D 65/08 20060101 B01D065/08 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 4, 2013 |
KR |
10-2013-0118753 |
Claims
1. A surface-modified membrane comprising: a membrane; and a
coating layer formed on a surface of the membrane in order to
improve fouling resistance and chemical resistance of the membrane,
wherein the coating layer comprises dopamine which implements the
thickness of the coating layer on the nanoscale in order to
suppress the permeation flow rate of the membrane from being
decreased before and after the coating layer is coated and provides
the coating layer with adhesion by which the coating layer is
stably bonded to the membrane, and a hydrophilic material which is
bonded to the dopamine through a secondary bond including a
hydrogen bond, or a cross-linked bond in order to suppress
durability of the coating layer from deteriorating, and imparts
hydrophilicity to the surface of the membrane in order to protect
the membrane from hydrophobic fouling materials.
2. The surface-modified membrane of claim 1, wherein the
hydrophilic material, which is bonded to the dopamine through the
cross-linked bond, is a poly ethylene glycol (PEG)-based material
comprising poly(ethylene glycol) methyl ether acrylate (PEGMEA),
poly(ethylene glycol) acrylate (PEGA), poly(ethylene glycol)
dimethacrylate (PEGDMA) and tetra(ethylene glycol) dimethacrylate
(TEGDM).
3. The surface-modified membrane of claim 1, wherein the
hydrophilic material, which is bonded to the dopamine through the
secondary bond comprising a hydrogen bond, is a water-soluble
molecule having an amphoteric hydrogen donor or hydrogen
acceptor.
4. The surface-modified membrane of claim 1, wherein the
hydrophilic material, which is bonded to the dopamine through the
secondary bond including a hydrogen bond, is a hydrophilic polymer
or a catecholamine-based water-soluble material.
5. The surface-modified membrane of claim 1, wherein the
hydrophilic material, which is bonded to the dopamine through the
secondary bond comprising a hydrogen bond, is a
poly(2-methacryloyloxyethyl phosphorylcholine) (MPC) polymer or an
amphiphilic copolymer having both hydrophilicity and
oleophilicity.
6. The surface-modified membrane of claim 1, wherein the coating
layer which is implemented by the dopamine has a thickness of 0.1
to 50 nm.
7. A method of modifying the surface of a membrane, the method
comprising: introducing a membrane of which the surface is to be
modified into a reactor; adding a mixed solution formed by adding a
hydrophilic material to a tris-buffer solution adjusted to a pH
range in which dopamine is reacted and stirring the resulting
mixture to the reactor; adding dopamine and an initiator which
induces a cross-linked bond between the hydrophilic material and
the dopamine to the reactor in a predetermined temperature range;
and forming a coating layer in which the dopamine and the
hydrophilic material are mixed on the membrane through thermal
crosslinking in the predetermined temperature range while injecting
oxygen into the reactor.
8. The method of claim 7, wherein the initiator is at least one
selected from the group consisting of lauroyl peroxide, ammonium
persulfate, potassium persulfate, and azobisisobutyronitrile
(AIBN).
9. The method of claim 7, wherein the pH range in which the
dopamine is reacted is pH 8 to pH 9, and the predetermined
temperature range is 60 to 80.degree. C.
Description
TECHNICAL FIELD
[0001] The present invention relates to a surface-modified membrane
in which the surface of the membrane is hydrophilically modified in
order to improve fouling resistance and chemical resistance of the
membrane, and a method of modifying the surface of the membrane for
implementing the surface-modified membrane.
BACKGROUND ART
[0002] In membranes used for water treatment, membrane fouling
occurs as membranes are used for a long period of time, and there
occur problems in a decrease in water permeation flow rate due to
membrane fouling and safety due to a long-term operation. Moreover,
these problems also cause an increase in overall operation costs of
the membrane.
[0003] Accordingly, various methods are used in order to reduce
membrane fouling. Examples of a representative method for reducing
membrane fouling include a surface-coating method of a hydrophilic
material and a chemical grafting method.
[0004] The surface-coating method of the hydrophilic material has
an advantage in that the membrane has excellent fouling resistance
during the initial period of operation, but has a disadvantage in
that there occurs a phenomenon in which a coating layer is peeled
off from the membrane during a long-period operation or when the
membrane is chemically cleaned for the continuous use of the
membrane.
[0005] Further, the chemical grafting method has an advantage in
that the method has excellent long-period stability compared to the
surface coating method of a hydrophilic material, but has a
disadvantage in that reaction conditions are stringent and it is
difficult to obtain a large area.
[0006] Accordingly, it may be considered to develop a technology of
modifying the surface of a membrane, which may overcome the
disadvantages present in the methods in the related art and improve
performance of the membrane.
DISCLOSURE OF THE INVENTION
[0007] Therefore, an object of the present invention is to suggest
a surface-modified membrane having a structure different from the
structure in the related art and a method of modifying the surface
of a membrane configured by a method different from the methods in
the related art.
[0008] Another object of the present invention is to provide a
technology of modifying the surface, which has excellent fouling
resistance and long-term stability for various supports.
[0009] To achieve these and other advantages and in accordance with
the purpose of the present invention, as embodied and broadly
described herein, there is provided a surface-modified membrane
according to an exemplary embodiment of the present invention,
including: a membrane; and a coating layer formed on the surface of
the membrane in order to improve fouling resistance and chemical
resistance of the membrane, in which the coating layer includes
dopamine which implements the thickness of the coating layer on the
nanoscale in order to suppress the permeation flow rate of the
membrane from being decreased before and after the coating layer is
coated and provides the coating layer with adhesion by which the
coating layer is stably bonded to the membrane, and a hydrophilic
material which is bonded to the dopamine through a secondary bond
including a hydrogen bond, or a cross-linked bond in order to
suppress durability of the coating layer from deteriorating, and
imparts hydrophilicity to the surface of the membrane in order to
protect the membrane from hydrophobic fouling materials.
[0010] According to an exemplary embodiment relating to the present
invention, the hydrophilic material, which is bonded to the
dopamine through the cross-linked bond, is a poly ethylene glycol
(PEG)-based material including poly(ethylene glycol) methyl ether
acrylate (PEGMEA), poly(ethylene glycol) acrylate (PEGA),
poly(ethylene glycol) dimethacrylate (PEGDMA) and tetra(ethylene
glycol) dimethacrylate (TEGDM).
[0011] According to anther exemplary embodiment relating to the
present invention, the hydrophilic material, which is bonded to the
dopamine through the secondary bond including a hydrogen bond, is a
water-soluble molecule having an amphoteric hydrogen donor or
hydrogen acceptor.
[0012] According to still another exemplary embodiment of the
present invention, the hydrophilic material, which is bonded to the
dopamine through the secondary bond including a hydrogen bond, is a
hydrophilic polymer or a catecholamine-based water-soluble
material.
[0013] According to yet another exemplary embodiment of the present
invention, the hydrophilic material, which is bonded to the
dopamine through the secondary bond including a hydrogen bond, is a
poly(2-methacryloyloxyethyl phosphorylcholine) (MPC) polymer or an
amphiphilic copolymer having both hydrophAccoilicity and
oleophilicity.
[0014] According to still yet another exemplary embodiment relating
to the present invention, the coating layer which is implemented by
the dopamine may have a thickness of 0.1 to 50 nm.
[0015] Further, in order to realize the aforementioned problems,
the present invention discloses a method of modifying the surface
of a membrane. The method of modifying the surface of a membrane
includes: introducing a membrane of which the surface is to be
modified into a reactor; adding a mixed solution formed by adding a
hydrophilic material to a tris-buffer solution adjusted to a pH
range in which dopamine is reacted and stirring the resulting
mixture to the reactor; adding dopamine and an initiator which
induces a cross-linked bond between the hydrophilic material and
the dopamine to the reactor in a predetermined temperature range;
and forming a coating layer in which the dopamine and the
hydrophilic material are mixed on the membrane through thermal
crosslinking in the predetermined temperature range while injecting
oxygen into the reactor.
[0016] According to an exemplary embodiment relating to the present
invention, the initiator is at least one selected from the group
consisting of lauroyl peroxide, ammonium persulfate, potassium
persulfate, and azobisisobutyronitrile (AIBN).
[0017] According to another exemplary embodiment relating to the
present invention, the pH range in which the dopamine is reacted is
pH 8 to pH 9, and the predetermined temperature range is 60 to
80.degree. C.
[0018] According to the present invention having the configuration
as described above, a coating layer may be formed on various
supports by being coated with dopamine and a hydrophilic
material.
[0019] Further, in the present invention, it is possible to form a
coating layer on the nanoscale, which is similar to a coating layer
coated with dopamine alone, and a stable coating layer may be
formed by strong adsorption capability of dopamine.
[0020] In addition, in the present invention, a coating layer
having fouling resistance and long-term stability may be formed on
a membrane by a hydrophilic material which is cross-linked to or
secondarily bonded to dopamine.
BRIEF DESCRIPTION OF THE DRAWINGS
[0021] FIG. 1a is a conceptual view for explaining membrane fouling
occurring in a membrane;
[0022] FIG. 1b is a graph for explaining a decrease in water
permeation flow rate by membrane fouling as the operation time of
the membrane is increased;
[0023] FIG. 2 is a conceptual view for explaining a technology of
cleaning a fouled membrane;
[0024] FIG. 3 is a partial cross-sectional view of a
surface-modified membrane relating to an exemplary embodiment of
the present invention;
[0025] FIG. 4 a flow-chart illustrating a method of modifying the
surface of the membrane relating to an exemplary embodiment of the
present invention;
[0026] FIGS. 5a and 5b are a scanning electron microscope
photograph which compares the membranes according to the present
invention before and after being surface-modified;
[0027] FIGS. 6a and 6b are a comparative graph for explaining the
hydrophilicity of the surface-modified membrane; and
[0028] FIGS. 7a to 9b are a comparative graph for explaining the
effects of modifying the surface of the membrane.
MODES FOR CARRYING OUT THE PREFERRED EMBODIMENTS
[0029] Reference will now be made in detail to the preferred
embodiments of the present invention, examples of which are
illustrated in the accompanying drawings. It will also be apparent
to those skilled in the art that various modifications and
variations can be made in the present invention without departing
from the spirit or scope of the invention. Thus, it is intended
that the present invention cover modifications and variations of
this invention provided they come within the scope of the appended
claims and their equivalents.
[0030] Description will now be given in detail of a drain device
and a refrigerator having the same according to an embodiment, with
reference to the accompanying drawings.
[0031] Hereinafter, a surface-modified membrane and a method of
modifying the surface of the membrane will be described in more
detail with reference to the accompanying drawings. In the present
specification, like reference numbers are used to designate like
constituents even though they are in different exemplary
embodiments, and the description thereof will be substituted with
the initial description. Singular expressions used herein include
plural expressions unless they have definitely opposite meanings in
the context.
[0032] FIG. 1a is a conceptual view for explaining membrane fouling
occurring in a membrane 10, and FIG. 1b is a graph for explaining a
decrease in water permeation flow rate by membrane fouling as the
operation time of the membrane is increased.
[0033] Membrane fouling refers to a phenomenon in which various
fouling sources are adsorbed on the pore 11 and surface of the
membrane 10.
[0034] Referring to FIG. 1a, pores 11 are formed in the membrane 10
used for water treatment, thereby filtering a solution to be
subjected to water treatment (bulk solution). As the operation time
of the membrane 10 passes, fouling sources are gradually adsorbed
on the surface and pore 11 of the membrane 10.
[0035] Examples of the fouling sources include sludge particles
having a large size and solutes having a relatively small size,
colloids corresponding to an intermediate size between the sludge
particles and the solutes, and the like. The sludge particles are
larger than the pores 11 of the membrane 10, and thus, are adsorbed
only on the surface of the membrane 10 (surface deposition), but
the colloids or the solutes not only are adsorbed on the surface of
the membrane 10 due to the size which is smaller than the pores 11,
but also permeate into the membrane 10 through the pore 11, thereby
plugging the pore 11 (pore plugging).
[0036] Membrane fouling causes a decrease in place for which a
material to be subjected to water treatment may permeate the
surface and pores of the membrane 10, thereby significantly
decreasing the permeation flow rate, and furthermore, significantly
increasing the operation time.
[0037] Referring to FIG. 1b, as the operation time for the membrane
is increased, membrane fouling occurs in the membrane, so that a
graph in which the permeation flow rate is gradually decreased is
illustrated.
[0038] The horizontal axis of the graph indicates time, and the
vertical axis of the graph indicates the amount of water permeated
(performance).
[0039] The amount of water permeated at the initiation time (0 h)
of operation of a poly(vinylidenedifluoride) (PVDF) membrane is
defined as a reference value of 100, and in 20 hours after
permeation of water is initiated when the operation time is
increased, the amount of water permeated is decreased to 0.1 or
less, which is about 1/2,000 level due to membrane fouling
occurring in the membrane.
[0040] In order to solve the problems caused by membrane fouling
occurring in the membrane as described above, a cleaning technology
of removing membrane fouling from the membrane is used, and will be
described with reference to FIG. 2.
[0041] FIG. 2 is a conceptual view for explaining a technology of
cleaning a fouled membrane 10.
[0042] The cleaning technology of the fouled membrane 10 is divided
into a physical method and a chemical method. First, the physical
method is a technology of removing a contaminant source adsorbed on
the surface of the membrane by using backwashing or aeration, and
the like. Moreover, the chemical method is a technology of removing
a fouling source adsorbed on the surface and pore 11 of the
membrane 10 by using a chemical detergent in which an oxidizing
agent and an acid are appropriately mixed.
[0043] Examples of the chemical method will be described with
reference to the following Table 1. NaOCl is an oxidizing agent,
and citric acid is an acid.
TABLE-US-00001 TABLE 1 Type Chemicals Conc. (%) Mitsubishi CIL
NaOCl 0.3 Citiric acid 0.2 Zenon CIP NaOCl 0.2 Citiric acid 0.2-0.3
Memcor CIP NaOCl 0.01 Citiric acid 0.2 Kubota CIL NaOCl 0.5 Citiric
acid 1
[0044] Referring to FIG. 2, when a new membrane begins to be used,
membrane fouling membranes are not adsorbed on the surface and
pores 11 of the membrane 10, but membrane fouling materials begin
to be adsorbed on the membrane 10 from the initial period of
operation of the membrane 10 (initial filtration). Furthermore, as
the operation time elapses, the amount of fouling materials
adsorbed on the membrane 10 is increased, so that a large amount of
membrane fouling materials are adsorbed on the surface and pores 11
of the membrane, respectively.
[0045] In the cleaning technology of removing the membrane fouling
materials, a physical method and a chemical method may be used in
combination with each other. First, a portion of membrane fouling
materials are removed by the physical method (physical cleaning),
and then subsequently, residual membrane fouling materials are
removed by the chemical method (chemical cleaning). The membrane 10
subjected to cleaning may be used again for water treatment and the
like because most of the membrane fouling materials are removed
from the membrane 10 even though the membrane 10 is not cleaned up
to the level of a new membrane 10.
[0046] The cleaning process is an essential process for using a
long-term membrane 10 in the operation of the membrane 10. However,
when the membrane 10 is frequently cleaned, the cleaning is
economically burdensome and causes a problem in that a coating
layer formed on the membrane 10 is peeled off.
[0047] The present invention has been made in an effort to overcome
the aforementioned problems, and it is an object of the present
invention to suggest a surface-modified membrane which may suppress
membrane fouling occurring in a membrane more fundamentally and a
method of modifying the surface of the membrane, and the present
invention will be described with reference to the following
drawings.
[0048] FIG. 3 is a partial cross-sectional view of a
surface-modified membrane 100 relating to an exemplary embodiment
of the present invention.
[0049] The surface-modified membrane 100 includes a membrane 110
and a coating layer 120 formed on the surface of the membrane 110.
FIG. 3 illustrates only the membrane 110 and the coating layer 120
for convenience of understanding of the present invention, but
pores (not illustrated) are naturally formed for the
surface-modified membrane 100 to function as a membrane.
[0050] The membrane 110 passes an object material through pores to
filter the object material. The present invention is not limited in
shape as long as the shape of the membrane 110 is formed in a form
which may modify the surface of a flat sheet membrane, a hollow
fiber membrane, and the like. The membrane 110 also serves as a
support which supports the coating layer formed on the surface.
[0051] The coating layer 120 is formed on the surface of the
membrane 110 so as to improve fouling resistance and chemical
resistance of the membrane 110. In the present invention, the
coating layer 120 formed on the surface of the membrane 110 is
formed by mixing dopamine with a hydrophilic material.
[0052] Dopamine allows the thickness of the coating layer to be
implemented on the nanoscale, and provides the coating layer 120
with strong adhesion.
[0053] The thickness of the coating layer is a factor which affects
the permeation flow rate of the membrane 110, and the permeation
flow rate is decreased as the thickness of the coating layer 120 is
increased. For example, when the coating layer 120 is formed of
only a poly ethylene glycol (PEG)-based hydrophilic material, there
is a problem in that the permeation flow rate of the membrane 110
significantly deteriorates due to the relatively large thickness of
the coating layer 120. However, dopamine, which is mixed with the
hydrophilic material to form the coating layer 120, may implement
the thickness of the coating layer 120 on the nanoscale, thereby
suppressing the permeation flow rate of the membrane 110 from being
decreased before and after the coating. The nanoscale thickness
means that the thickness of the coating layer 120 is in a range of
0.1 to 50 nm. More preferably, the thickness of the coating layer
120 may be in a range of 1 to 20 nm.
[0054] When the coating layer 120 is formed of only a poly ethylene
glycol (PEG)-based hydrophilic material, the type of support on
which the coating layer 120 may be formed is limited and the
overall durability of the membrane 110 is also limited because the
coating layer 120 is not strongly adsorbed on the membrane 110.
Dopamine provides the coating layer 120 with strong adhesion by
which the coating layer 120 is stably bonded to the membrane 110,
and allows the coating layer 120 to be formed on various types of
supports, and prevents the coating layer 120 from being peeled off
from the membrane 110, thereby improving the overall durability of
the surface-modified membrane 100.
[0055] The hydrophilic material is boned to dopamine through a
secondary bond including a hydrogen bond, or a cross-linked bond,
thereby suppressing the durability of the coating layer 120 from
deteriorating and imparting hydrophilicity to the surface of the
membrane 110.
[0056] The cross-linked bond or the secondary bond has relatively
strong bonding power, and thus, may improve durability of the
coating layer 120 when a hydrophilic material is bonded to dopamine
through the cross-linked bond or the secondary bond. In particular,
when the surface-modified membrane 100 is operated for a long
period of time, the hydrophilic material, which is strongly bonded
to dopamine through the cross-linked bond or the secondary bond,
physically and chemically maintains durability of the coating layer
120.
[0057] Most of the membrane fouling materials are hydrophobic
materials, and thus, may protect the membrane 110 from hydrophobic
fouling materials when imparting hydrophilicity to the surface of
the membrane 110.
[0058] Hereinafter, examples of the hydrophilic material which may
be cross-linked or secondarily bonded to dopamine will be
described.
[0059] The hydrophilic material, which is bonded to the dopamine
through the cross-linked bond, is a poly ethylene glycol
(PEG)-based material including poly(ethylene glycol) methyl ether
acrylate (PEGMEA), poly(ethylene glycol) acrylate (PEGA),
poly(ethylene glycol) dimethacrylate (PEGDMA) and tetra(ethylene
glycol) dimethacrylate (TEGDM).
[0060] The molecular structures of the poly ethylene glycol
materials exemplified above are represented by the following
Chemical Formulae 1 to 4.
##STR00001##
[0061] The hydrophilic material, which is bonded to the dopamine
through the secondary bond including a hydrogen bond, includes a
water-soluble molecule having an amphoteric hydrogen donor or
hydrogen acceptor. The water-soluble molecule having an amphoteric
hydrogen donor or hydrogen acceptor is represented by the following
Chemical Formulae 5 to 8. In Chemical Formulae 5 to 8, A and B are
a hydrogen donor and represented by Chemical Formulae 9 and 10,
respectively, and C and D are a hydrogen acceptor and represented
by Chemical Formulae 11 and 12, respectively.
##STR00002## ##STR00003##
[0062] The hydrophilic material, which is bonded to the dopamine
through the secondary bond including a hydrogen bond, includes a
hydrophilic polymer or a catecholamine-based water-soluble
material. The hydrophilic polymer and the catecholamine-based
water-soluble material are represented by the following Chemical
Formulae 13 to 19.
##STR00004##
[0063] The hydrophilic material, which is bonded to the dopamine
through the secondary bond including a hydrogen bond, includes a
poly(2-methacryloyloxyethyl phosphorylcholine) (MPC) polymer or an
amphiphilic copolymer having both hydrophilicity and oleophilicity.
The poly(2-methacryloyloxyethyl phosphorylcholine) (MPC) polymer is
represented by the following Chemical Formula 20, and the
amphiphilic copolymer having both hydrophilicity and oleophilicity
is represented by the following Chemical Formula 21.
##STR00005##
[0064] Hereinafter, a method of modifying the surface of a membrane
will be described.
[0065] FIG. 4 a flow-chart illustrating a method of modifying the
surface of the membrane relating to an exemplary embodiment of the
present invention. However, the surface-modified membrane as
described above is not necessarily formed by the method described
in FIG. 4.
[0066] In order to modify the surface of a membrane, first, a
membrane of which the surface is to be modified is introduced into
a reactor (S100).
[0067] The membrane of which the surface is to be modified serves
as a support layer which supports a coating to be formed on the
surface of the membrane. In the present invention, since various
supports may be used by adding dopamine, a polymer or metal and the
like may be used as a material for the support. Accordingly, it is
possible to overcome the material limitation of the support.
[0068] Next, a mixed solution formed by adding a hydrophilic
material to a tris-buffer solution adjusted to a pH range in which
dopamine is reacted and stirring the resulting mixture is added to
the reactor (S200).
[0069] The tris-buffer solution adjusted to a pH range in which
dopamine is reacted needs to be prepared in advance before the
hydrophilic material is added to the solution, and the pH of the
solution is adjusted to pH 8 to pH 9 in which dopamine is reacted
by adding an acidic solution such as tris-HCl to water and
additionally adding a basic solution such as NaOH thereto.
[0070] Furthermore, a mixed solution is produced by adding a
hydrophilic material such as poly ethylene glycol to the
tris-buffer solution with the pH adjusted and stirring the
resulting mixture, and then the mixed solution is added to the
reactor into which the membrane has been introduced.
[0071] Subsequently, dopamine and an initiator which induces a
cross-linked bond between the hydrophilic material and the dopamine
are added to the reactor in a predetermined temperature range
(S300).
[0072] As the dopamine, dopamine hydrochloride (Dopa-HCl) and the
like may be used. As the initiator, it is possible to use at least
one selected from the group consisting of lauroyl peroxide,
ammonium persulfate, potassium persulfate, and
azobisisobutyronitrile (AIBN), which may induce a cross-linked bond
between the hydrophilic material and the dopamine. The molecular
structure of each initiator is represented by the following
Chemical Formulae 22 to 25.
##STR00006##
[0073] Finally, a coating layer in which the dopamine and the
hydrophilic material are mixed is formed on the membrane through
thermal crosslinking in the predetermined temperature range while
injecting oxygen into the reactor (S400).
[0074] Through thermal crosslinking, dopamine and the hydrophilic
material form a cross-linked bond are bonded to each other, thereby
forming a coating layer on the surface of the membrane. After the
thermal crosslinking reaction is completed, it is preferred that
the surface-modified membrane is additionally washed with
water.
[0075] Hereinafter, the membranes before and after being
surface-modified will be compared with each other with reference to
FIGS. 5a and 5b.
[0076] FIGS. 5a and 5b are a scanning electron microscope
photograph which compares the membranes according to the present
invention before and after being surface-modified.
[0077] FIG. 5a is a photograph of the membrane before being
surface-modified, and FIG. 5b is a photograph of the membrane after
being surface-modified. When FIGS. 5a and 5b are compared with each
other, it can be confirmed that there is no significant change on
the surface of the membrane. Through this, it can be inferred that
the coating layer formed on the membrane has been formed on the
nanoscale, and a decrease in permeation flow rate of the membrane
before and after the coating is also very limiting.
[0078] Hereinafter, specific exemplary embodiments of the method of
modifying the surface of the membrane described in FIG. 4 will be
described in comparison with the Comparative Example, and the
effects of the present invention will be described with reference
to FIGS. 6a to 9b.
EXAMPLES
[0079] The materials and concentrations required for the reaction
in the present Example are each shown in Table 2.
TABLE-US-00002 TABLE 2 Material Concentration pH-Adjusted Buffer
Solution (Trizma hydrochloride, 15 mmol/L Tris-HCl) Dopamine
(hydrochloride, Dopa-HCl) 1 mg/mL Hydrophilic material
(poly(ethylene glycol) 1 mg/mL diacrylate (PEGDA)) Initiator
(Potassium persulfate (KPS)) 0.1 mg/mL
[0080] First, a mixed solution of a tris-buffer solution for being
introduced into a reactor and a hydrophilic material is
prepared.
[0081] 15 mM of Tris-HCl is added to ultra-pure water and the
resulting mixture is sufficiently mixed. When the tris-HCl is
completely dissolved, an NaOH solution is added thereto to adjust
the pH to pH 8.5 in which dopamine is reacted, thereby preparing a
tris-buffer solution. Poly ethylene glycol (PEG) is added to the
tris-buffer solution prepared, and the resulting mixture was
stirred for 24 hours or more to prepare a mixed solution.
[0082] Next, the membrane of which the surface is to be modified is
fixed on the bottom of the reactor, and then, the mixed solution
previously prepared is added thereto. The temperature in the
reactor is adjusted to 65.degree. C. or more, and an initiator KPS
and dopamine Dopa-HCl were simultaneously added thereto.
[0083] It is possible to prepare a surface-modified membrane to be
implemented in the present invention by carrying out thermal
crosslinking for 30 minutes while injecting ultra high pure oxygen
into the reactor at a rate of 0.5 L/min, and performing washing
with ultra-pure water for 1 hour or more after the reaction is
completed.
Comparative Example
[0084] In the Comparative Example, a coating layer is formed by
only an oxidation reaction without mixing a hydrophilic solution.
The materials and concentrations required for the reaction in the
present Comparative Example are each shown in Table 3.
TABLE-US-00003 TABLE 3 Material Concentration pH-Adjusted Buffer
Solution (Trizma 15 mmol/L hydrochloride, Tris-HCl) Dopamine
(hydrochloride, Dopa-HCl) 2 mg/mL
[0085] First, the tris-buffer solution is prepared, but the
hydrophilic solution is not mixed unlike in the Example previously
explained. For the tris-buffer, 15 mM of tris-HCl is added to
ultra-pure water and the mixture is sufficiently mixed. The pH is
adjusted to 8.5 by completely dissolving tris-HCl, and then adding
the NaOH solution thereto.
[0086] Subsequently, the membrane is fixed on the bottom of the
reactor, and then the tris-buffer solution is added thereto.
Moreover, dopamine is added, the oxidation reaction is carried out
for 30 minutes while injecting ultra high pure oxygen into the
reactor at a rate of 1 L/min, and then the membrane is washed with
ultra-pure water for 1 hour or more.
[0087] Hereinafter, the surface-modified membrane previously
explained and the effects of the method of modifying the surface of
the membrane will be described with reference to the drawings.
[0088] FIGS. 6a and 6b are a comparative graph for explaining the
hydrophilicity of the surface-modified membrane.
[0089] The water contact angle indicates an angle between a water
drop and the surface, and means that the lower the value is, the
more hydrophilic the surface of the support is.
[0090] The graph illustrated in FIG. 6a compares the case where
polyacrylonitrile (PAN350) and polyethersulfone (PES900) are not
each surface-modified (PAN350 and PES900), the case where PAN350
and PES900 are surface-modified with only dopamine (PAN350 D and
PES900 D), and the case where PAN350 and PES900 are
surface-modified by mixing dopamine with a hydrophilic material
(PAN350 D/P and PES900 D/P).
[0091] It can be confirmed that the membrane modified with dopamine
is more hydrophilic than the case where the surface of the membrane
is modified, and the membrane obtained by mixing dopamine with the
hydrophilic material and modifying the surface is more hydrophilic
than the case where the surface of the membrane is modified with
only dopamine.
[0092] The graph illustrated in FIG. 6b compares the case where
polysulfone (PS20) and polyvinyldifluoride (PVDF350) are not each
surface-modified (PS20 and PVDF350), the case where PS20 and
PVDF350 are surface-modified with only dopamine (PS20 D and PVDF350
D), and the case where PS20 and PVD350 are surface-modified by
mixing dopamine with a hydrophilic material (PS20 D/P and PVDF350
D/P).
[0093] Even in FIG. 6b, it can be confirmed likewise as in FIG. 6a
that the membrane modified with dopamine is more hydrophilic than
the case where the surface of the membrane is modified, and the
membrane obtained by mixing dopamine with the hydrophilic material
and modifying the surface is more hydrophilic than the case where
the surface of the membrane is modified with only dopamine.
[0094] Since the fact that the surface-modified membrane indicates
hydrophilicity means that the membrane may be protected from
hydrophobic fouling materials, it can be confirmed from FIGS. 6a
and 6b that the present invention may improve fouling resistance of
the membrane by a coating layer.
[0095] FIGS. 7a to 9b are a comparative graph for explaining the
effects of modifying the surface of the membrane.
[0096] FIGS. 7a and 7b compare the case where polyvinyldifluoride
(PVDF) is not surface-modified (PVDF Pristine), the case where
polyvinyldifluoride (PVDF) is surface-modified with only dopamine
(PVDF PDOPA), and the case where polyvinyldifluoride (PVDF) is
surface-modified by mixing dopamine with a hydrophilic material
(PVDF PDOPA/XPEO), FIG. 7a compares the changes in water flux of
the membrane over the time of operation, and FIG. 7b sets the water
flux of the membrane at the time (0 min) of initiating the chemical
cleaning (NaOCl) as a reference value of 1.0 and compares the flux
ratios over time.
[0097] FIGS. 8a and 8b compare the case where polysulfone (PSF) is
not surface-modified (PSF Pristine), the case where polysulfone
(PSF) is surface-modified with only dopamine (PSF PDOPA), and the
case where polysulfone (PSF) is surface-modified by mixing dopamine
with a hydrophilic material (PSF PDOPA/XPEO), FIG. 8a compares the
changes in water flux of the membrane over the time of operation,
and FIG. 8b sets the water flux of the membrane at the time (0 min)
of initiating the chemical cleaning (NaOCl) as a reference value of
1.0 and compares the flux ratios.
[0098] FIGS. 9a and 9b compare the case where polyethersulfone
(PES) is not surface-modified (PES Pristine), the case where
polyethersulfone (PES) is surface-modified with only dopamine (PES
PDOPA), and the case where polyethersulfone (PES) is
surface-modified by mixing dopamine with a hydrophilic material
(PES PDOPA/XPEO), FIG. 9a compares the changes in water flux of the
membrane over the time of operation, and FIG. 9b sets the water
flux of the membrane at the time (0 h) of initiating the chemical
cleaning (NaOCl) as a reference value of 1.0 and compares the flux
ratios.
[0099] Referring to FIGS. 7a, 8a, and 9a, it can be confirmed that
the surface-modified membrane according to the present invention
has a minimal change in rejection when the case where the surface
is not modified is compared with the case where the surface is
coated with only dopamine, and thus, the coating layer is formed on
the nanoscale in which the pores of the membrane are not clogged,
and that a decrease in water flux over time is also limiting, and
thus, fouling resistance is improved.
[0100] Further, referring to FIGS. 7b, 8b, and 9b, it can be
confirmed that the surface-modified membrane according to the
present invention has the smallest change in water permeation rate
of the coating layer before and after the chemical cleaning when
the case where the surface is modified is compared with the case
where the surface is coated with only dopamine, and thus, chemical
resistance and fouling resistance are improved, and the structural
stability of the coating layer is improved.
[0101] The surface-modified membrane and the method of modifying
the surface of the membrane as described above are not limited by
the configurations and methods of the exemplary embodiments as
described above, but the exemplary embodiments may also be
configured by selectively combining a whole or part of the
exemplary embodiments, such that various modifications can be
made.
[0102] The present invention may be used in various industrial
fields which are associated with a membrane for water
treatment.
* * * * *